One-dimensional nanospace confinement effects on the chemical properties of organic molecules in carbon nanotubes: Quantum chemical calculation analyses

Abstract

We performed dispersion-corrected density functional theory (DFT) calculations to investigate the energetically stable structures of armchair (m,m) carbon nanotubes containing π-conjugated molecules, such as methyl-terminated thiophene oligomers, p,p′-dimethyaminonitorostilbene (DANS) molecules, and triiodobenzene. The stability of such tube-based host-guest structures was analyzed by using their stabilization energy, which consisted of three terms. These analyses found that the long-range interaction energy between guest and a host, mainly originating from π–π and CH–π interactions, and the deformation energy of the guest molecule are what mostly control the stability of the tube-based host-guest structures considered in this paper. The long-range interactions mainly cause nanospace confinement effects in tube-based host-guest structures. To strengthen the long-range attraction interactions, a π-conjugated molecule and its aggregates inside a tube are substantially deformed, which costs energy compared to the corresponding optimized structures without surrounding tubes. Accordingly, we found a substantial impact of nanotube confinement in determining the structure of a guest and its aggregates. These structures play a dominant role in electronic properties (e.g. optoelectronic properties in thiophene oligomers and nonlinear second-order nonlinear properties in DANS molecules), and therefore nanospace confinement effects can be used to change the electronic properties of π-conjugated molecules inside a nanotube by changing its diameter.